Flash memory devices (e.g., NAND flash devices) have become increasingly popular in data storage for computer systems, mobile devices, and consumer devices (e.g., cameras). Solid-state drives (SSDs) using flash devices have now become important in many data storage applications. The life expectancy and data quality of flash devices depend on several factors such as data write rate, program and erase cycles, and environmental conditions (e.g., temperature). Applications using flash devices may have various requirements. For data intensive applications such as real-time databases with frequent updates, it is important to have long-life flash devices. In contrast, applications that have short commercial time span and infrequent data updates such as mobile phones may not need long-life flash devices. Accordingly, there exists a need to classify flash devices according to their quality and reliability so that they may be properly used in a variety of applications.
Current techniques for classifying flash devices have a number of drawbacks. Manufacturers of flash devices do not provide grades for their flash devices. While they do provide test information on their flash devices (e.g., initial valid blocks when first shipped, Total Bytes Written or Tera Bytes Written), this information may not be useful because it does not provide an accurate picture of the quality of the devices. In addition, most flash devices have comparable number of invalid blocks or Total Bytes Written or Tera Bytes Written (TBW) and therefore it is difficult to distinguish them. Furthermore, each manufacturer may have its own test parameters and therefore classifying flash devices that are manufactured by different manufacturers may not be accurate.